MARS

In the Solar System, one of the old planets, and the fourth in the order of distance from the sun. The mean distance of Mars from the sun is 1-5236923, the mean distance of the earth from the sun being 1: it is, consequently, about 142,000,000 of miles. Mars performs his mean sidereal revolution in 6869796458 mean solar days, and his synodical revolution (that is, returns to the same position in respect to the earth and sun) in 779.936 days. His orbit, at the beginning of the present century was inclined to the ecliptic in an angle of 1° 51' 6"; and its eccentricity is.093307, half the major axis being unit. His apparent diameter varies from 36" at his greatest, to 18-28 ' at his least distance from the earth. At his mean distance the apparent diameter is 6-29"; whence the true diameter is found equal to -517, that of the earth being unit, or about 4100 miles. Mars has a rotation about his axis which is performed in 24 h. 39 m. 21 sec. The inclination of the axis to the ecliptic is 30° 18'. When the opposition of Mars takes place at the time he is. near the aphelion of his orbit he is then at his least distance from the earth, and presents an interesting appearance when seen through a powerful telescope. "In this planet," says Sir John Herschel, " we discern, with perfect distinctne , the outlines of what may be.continents and seas. Of these the former are distinguished by that ruddy colour which characterizes the light of this planet (which always appears red and fiery), and indicates, no doubt, an ochrey tinge in the general soil, like what the red sandstone districts on the earth may po ibly offer to the inhabitants of Mars, only more decided. Contrasted with this (by a general law in optics) the seas, as we may call them, appear greenish. These spots, however, are not always to be seen equally distinct, thoueh, when seen, they offer always the same appearance.This may arise from the planet not being entirely destitute of atmosphere and clouds; and what adds greatly to the probability of this is the appearance of brilliant white spots at its poles, which have been conjectured, with a great deal of probability, to be snow; as they disappear when they have been long exposed to the sun, and are greatest when just emerging from the long night of their polar win ter." (Astronomy, Cab. Cyc.) See Planet. MARS, or [s. 736]